202 PATHOGENIC BACTERIA. organisms. Wertheim cultivated the gonococcus from a case of chronic urethritis of two years' standing, and proved its virulence by producing with it gonorrhea in a human being. The organisms are generally found within the pus-cells (Fig. 58) or attached to the surface of epithelial cells, and should always be sought for as diagnostic of gonorrhea, especially as urethritis some- times is caused by other organisms, as the Bacillus coli cornmunis1 and the Staphylococcus pyogenes. The cultivation of the gonococcus is not an easy task, but one which requires considerable bacteriologic skill. Wertheim accomplished it by diluting a drop of the pus in a little liquid hitman blood-serum, then mixing this with an equal part of melted 2 per cent, agar-agar at 40° C., and pouring into Petri dishes. As soon as the media became firm the dishes were stood in the incubator at 37° C., and in twenty-four hours the colonies could be observed. Those upon the surface showed a dark centre, around which a delicate granular zone could be made out. When one of these colonies is transferred to a tube of human blood-serum or the above mixture obliquely co- agulated, isolated little gray colonies occur; later these become confluent and produce a delicate smeary layer upon the medium. The main growth is surrounded by a thin, veil-like extension which gradually fades away into the medium. A slight growth occurs upon the water of condensation, Turro says that the gonococci may also be cultivated upon acid gelatin, upon gelatin containing acid urine, and also in acid urine itself, in which the gonococci grow near the surface, while the pus-cocci which may be mixed with them sink deeper into the medium. His work has not been confirmed by other investigators. Heiman,2 who made an extensive series of culture-ex- 1 Van der Pluyn and Loag: Centralbl f. Bakt. u. Parasitenk., Bd. xvii., Nos. 7, 8, Feb. 28, 1895, p. 233. 2 Med. Record, Dec. 19, 1886.